BMI Calculator

BMI Calculator for Teenagers

BMI is calculated differently for teenagers than for adults. Because body composition changes rapidly during puberty, teen BMI must be plotted on age- and sex-specific growth charts using percentiles rather than fixed categories.

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Use our bmi calculator with these considerations in mind.

Open BMI Calculator

Key Considerations

Teen BMI uses percentiles, not adult categories (18.5-24.9 does not apply)
Healthy weight: 5th-84th percentile for age and sex
Overweight: 85th-94th percentile
Obese: 95th percentile and above
Underweight: below 5th percentile
BMI changes naturally during puberty — track trends, not single measurements

Specific Adjustments

Early Puberty

Body composition changes rapidly. BMI may fluctuate as height and weight develop at different rates. This is normal.

Athletic Teens

Muscular teenagers may have higher BMI percentiles without excess body fat. Consider overall fitness and health, not just BMI.

Tips for Best Results

1Use the NHS BMI percentile calculator specifically designed for children and teenagers

2Track BMI percentile over time rather than reacting to single measurements

3Never use BMI as a reason to restrict a teenager's food intake — speak to a GP first

4Focus on healthy habits (balanced eating, regular activity) rather than weight numbers

5If concerned about your teen's weight, consult your GP or school nurse for professional guidance

Frequently Asked Questions

Why is teen BMI different from adult BMI?

During growth, "normal" BMI changes with age and differs between boys and girls. A BMI of 22 might be overweight for a 12-year-old but healthy for a 17-year-old. Percentile charts account for these changes.

Where can I check my teen's BMI percentile?

The NHS provides a healthy weight calculator for children aged 2-18 at nhs.uk. It plots BMI against age- and sex-specific growth charts and provides a percentile result.

Should teenagers worry about their BMI?

Teenagers should focus on healthy habits rather than BMI numbers. BMI is a screening tool for healthcare professionals. If a GP or school nurse raises concerns, they will provide appropriate, sensitive guidance.